1. Field of the Invention
The present invention relates to a reversible thermosensitive recording material capable of recording and erasing images repeatedly by utilizing its property that the transparency can be changed reversibly from a transparent state to an opaque state, and vice versa, depending upon the temperature thereof.
2. Discussion of Background
There are conventionally proposed reversible thermosensitive recording materials capable of performing reversible recording and deleting images, which comprise a support and a reversible thermosensitive layer in which an organic low-molecular-weight material, such as a higher alcohol or a higher fatty acid, is dispersed in a matrix resin such as polyester and vinyl chloride, as disclosed, for example, in Japanese Laid-Open Patent Applications 54-119377 and 55-154198. In the above-mentioned reversible thermosensitive recording materials, the formation of images and the erasure thereof in the thermosensitive recording layer thereof can be carried out by utilizing the property of the reversible thermosensitive recording materials that the transparency of the recording layer of the materials changes depending upon the temperature thereof.
Such conventional reversible thermosensitive recording materials, however, have the shortcoming that an opaque state of the reversible thermosensitive recording layer is changed to a transparent state within a range of as narrow as 2.degree. C. to 4.degree. C. Therefore it is difficult to control the temperature at which a partially opaque reversible thermosensitive recording material is totally changed to a transparent state, or a totally opaque reversible thermosensitive recording material is changed to a partially transparent state to form transparent images thereon. Furthermore, the conventional reversible thermosensitive recording materials are not durable in the repeated operation of forming and erasing the images.
Furthermore, the conventional reversible thermosensitive recording materials have the shortcoming that the contrast of an image area to a background is affected by the amount of the organic low-molecular-weight material contained in the matrix resin. More specifically, when the amount ratio of the organic low-molecular-weight material to the matrix resin is low, the density of a-milky white opaque area is low. Reversely, when the amount ratio of the organic low-molecular-weight material to the matrix resin is high, the transparency is insufficient although the density of the milky white opaque area is sufficiently high.
The contrast of the image area to the background is also degraded when a black support which is colored in black is employed.
The applicants of the present invention have found that the contrast of the image area to the background in the reversible thermosensitive recording layer can be upgraded by attaching a light reflection layer to the reversible thermosensitive recording layer, as shown in Japanese Laid-Open Patent Application 1-14079. However, when a light reflection layer made of a metal is directly attached to the thermosensitive recording layer, the adhesion of the light reflection layer to the thermosensitive recording layer is so poor that the light reflection layer is easily peeled off the thermosensitive recording layer. Accordingly, the durability of the reversible thermosensitive recording material is shortened. Furthermore, the reflectance becomes too high to be used in practice when a metal such as aluminum is deposited on an even surface of the support, so that reflected images become unclear.